The invention relates to a self-dumping centrifugal separator drum having a piston valve defining one end of the separating and solids chamber for the control of the ejection apertures in the drum periphery, permitting the performance of dumping operations selectively and in a time-independent manner, the closing chamber being supplied with control fluid in a known manner, and fluid-operated valves being installed in the control fluid outlet passages.
A centrifugal drum separator of such construction is known, for example, from German Pat. No. 2,041,371 (U.S. Pat. No. 3,754,701) and serves for the clarification or separation of liquids containing solids, the closing chamber filled with control fluid having a larger radial expanse than the inner chamber of the drum, so that, when the chamber is completely filled, the closing pressure acting from this side on the piston valve is always greater than the pressure of the drum charge acting in the opening sense from the other side. For the purpose of solids ejection, control fluid is let out of the closing chamber through fluid-controlled valves with the drum at full rotatory speed, and the closing pressure is thus relieved. Under the pressure of the drum charge the piston valve then moves into the open position, opening the ejection apertures. Depending on the nature and consistency of the solids which are to be separated, so-called partial dumping can then be performed at shorter intervals of time or full dumping can be performed at greater intervals. In the performance of partial dumping, the drum is opened only slightly and briefly by letting only so much control fluid out of the closing chamber through valves that only a portion of the solids collected in the solids chamber is ejected, while the remainder of the solids stays in the drum as a safety ring. This prevents an excessively great amount of liquid from being thrown out of the drum with the solids and being wasted.
These discharge systems, however, run into difficulty in the removal of solids which are caked on the inner wall of the drum. When full dumping is performed, there is the danger that the solids will not be full discharged, so that imbalance damage might occur, and when partial dumping is performed, the discahrge gap is so small that most of the solids remain stuck in the drum and only liquid emerges. Even very rapidly operating control-water systems which open a very large gap for only a very brief time for the partial dumping operation have limitations due to the inertia of the system. Such a control system is known, for example, from German Offenlegungsschrift No. 2,704,903 (U.S. Pat. No. 4,151,951).